Use mojo volume interfaces for mash and classic ash.

chrome/browser/chromeos/extensions/extension_volume_observer.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_VOLUME_OBSERVER_H_
+#define CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_VOLUME_OBSERVER_H_
+
+#include "base/macros.h"
+#include "chromeos/audio/cras_audio_handler.h"
+
+namespace chromeos {
+
+// Dispatches extension events in response to volume events.
+class ExtensionVolumeObserver : public CrasAudioHandler::AudioObserver {
+ public:
+  // This class registers/unregisters itself as an observer in ctor/dtor.
+  ExtensionVolumeObserver();
+  ~ExtensionVolumeObserver() override;
+
+  // CrasAudioHandler::AudioObserver:
+  void OnOutputNodeVolumeChanged(uint64_t node_id, int volume) override;
+  void OnOutputMuteChanged(bool mute_on, bool system_adjust) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ExtensionVolumeObserver);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_EXTENSION_VOLUME_OBSERVER_H_